How To fix broken tip of Kainuun puukko

[Deboelduncan]

by a stupid accident I broke off a tiny bit of the tip of my custom Kainuun puukko hunting knife by Marko Lindela. It also has what looks like tiny specks of rust to me, how would you guys recommend repairing it and removing the rust? The blade is made from silversteel (115CrV3).

[/IMG] ( https://imgur.com/XzHNOX4 )

[/IMG] ( https://imgur.com/3PBxWbP )

 

[Obsessed with Edges]

Easy fix. Use a coarse stone in SiC (silicon carbide) or aluminum oxide; something around 120-220 works well. Turn the blade over, edge-up, and grind the spine of the blade near the broken tip, keeping the blade as low to the stone as you can, to keep the tip as acutely pointy as possible. Use tip-trailing strokes along the length of the stone, i.e., with the knife moving in opposite direction to where the tip is pointing. The idea is to grind down the spine until it intersects the sharp cutting edge in a nice, sharp & pointy tip. If the cutting edge is already well-sharpened, that's all it takes. Seems intimidating at first; but it's really surprisingly simple once you've done it for the first time.

The steel in that blade doesn't present any significant wear-resistance in the form of very hard carbides. So the grinding should be that much easier on the stones mentioned. I've also done the same thing on an aluminum oxide grinding belt (120-grit), with the belt cut and glued flat to a hard surface (hardwood, etc). The extra length of the belt, cut and laid flat, makes grinding go a lot faster, although it shouldn't take very long anyway on your knife, with that relatively small amount of damage.

You can use a block of wood or something similar to press onto the cutting edge near the tip, in order to provide a safe place for your hands to apply some pressure in the grinding. I've also used a wine cork (synthetic) for the same purpose; but you need to watch it as you work, as a sharp cutting edge will press through the cork as you work. So be careful.

A little bit of rust can usually be scrubbed off with some mineral oil and steel wool, or polished away with some metal polish (Flitz, Simichrome, etc). OR, use some Bar Keepers Friend powder, mixed to a paste with water and applied to the rust spots for 30 seconds - 1 minute, then rinsed off. Make sure you rinse it well, as the oxalic acid in the Bar Keepers Friend powder will etch the steel on it's own, if left on too long. If you don't mind some fine-satin scratches, a so-called 'rust eraser' can be used to scrub the rust off. It's basically SiC grit embedded in a rubbery binder, like a pencil eraser. It WILL alter the finish on the steel, leaving a fine satin finish. More visible on a polished blade; but on most factory finishes, it won't stand out too much.

 

[Alberta Ed]

Glad to see you're using that elegant puukko. A little ding like that isn't significant; most well-used blades will incur similar wear.

 

[Deboelduncan]

Thank you so much for the help! I'll fix it completely as soon as my finals are over
just to make sure I don't do it wrong, this is how you recommend sharpening it, right?

[/IMG] ( https://imgur.com/uEZ6eFv )

and yes, real happy with the knife! I didn't sharpen it myself yet, still has a good edge on it.

 

[Obsessed with Edges]

Thank you so much for the help! I'll fix it completely as soon as my finals are over
just to make sure I don't do it wrong, this is how you recommend sharpening it, right?

[/IMG] ( https://imgur.com/uEZ6eFv )

and yes, real happy with the knife! I didn't sharpen it myself yet, still has a good edge on it.

That looks basically like the right idea. I'd hold the handle as low as possible, so the angle toward the tip of the blade more closely follows the line of the spine, toward the tip. As drawn in your picture, the arrow would seem to indicate a steeper-angled, more abrupt change in the tip profile. It's up to you, what you want the tip to look like. But that's how I'd go about it.

To explain further, I'd generally start by placing the spine's mid-portion (or forward 1/3rd or so) on the stone, beginning the tip-trailing pass. As you make the pass over the stone, gradually lift the handle so you're grinding in a shallow arc toward the tip. Don't lift the handle too high or too quickly; just gradual enough that the newly-ground portion of the spine will smoothly and elegantly arc toward the tip of the blade. Don't rush the process or try to grind off too much in one pass; keep everything steady, smooth and controlled.

 

[bgentry]

I respect David's knowledge and opinion. But in this case I disagree rather strongly. Spine grinding the blade will change it's profile a bit. It's not a huge big deal, but the point won't be in line with the spine any more. This bugs me a bit. Spine grinding is ok for fixing a *tiny* little bit of tip rounding. But for something more major like this, I would grind the edge instead.

It's harder to do and requires a bit of finesse. Take a marker and draw an arc from where the spine meets the end of the blade, down the blade into the edge. The longer you make the arc, the more gradual the blend will be. You just have to eyeball this to blend the curve so that it looks natural on this blade.

When you are done the spine will still be flat. The point will be in line with the spine. The curve at the end of the blade will be reshaped a little. But it should look just fine as long as you blend it a bit.

I can probably dig up an illustration if necessary.

Brian.

 

[Obsessed with Edges]

This is what I had in mind, for reshaping the tip. I saved a copy of the OP picture of the drawing, and highlighted in red the portion I'd grind away, more or less in the 'arc' I described. The pic is general in the concept of it; so the arc can be extended further back, to more streamline the profile toward the tip, if desired. It makes for a cleaner looking tip that way, and sharper too.

 

[Obsessed with Edges]

Save the edge's thinner cutting geometry; it's a big part of what makes these knives cut so well in the first place. It's so much easier done by grinding the spine, without worrying about reshaping the cutting edge, which is already good and doesn't need fixing; it'll cut much better as well, at the tip, when done. The edge is already what it needs to be; there's no sense in altering it to re-point the tip.

Grinding from the edge up, to meet the spine, will only leave the edge near the tip much thicker, which makes it harder to keep it cutting well in the long run.

Pics below are of a tip I repaired on a ZDP-189 blade (Kershaw Leek). Done in the same manner as I described above, although I used an Aluminum Oxide (Zirconia-Alumina) 3" x 21" 120-grit grinder belt, cut at the seam and glued flat on a piece of wood, instead of a stone. This gave me 21" of abrasive length to work upon, so it went pretty fast.

Before:

After the repair:

 

[Groundhogsniper]

I would also repair this knife as Brian described.
I have fixed several broken tips like that and properly done you’d be hard pressed to detect the repair with just a tiny bit broken off like th OP’s knife.

 

[Chris "Anagarika"]

I think Brian raises concern about the blade profile being a puukko has to have flat spine. However it’s up to OP how he wants the blade to end up, and depend on his use case.

David’s method will be easier but change the spine profile. Brian’s method will keep the spine flat but requires more work to grind the scandi from belly to tip, basically like making the knife for the first time.
On a drop point, spear or leaf shape blade, I’d definitely follow David’s method, easier to do.
However, if keeping true puukko profile is important, should use Brian’s. Any option to send back to maker for repair?

 

[Obsessed with Edges]

The flat spine profile can still be maintained, just by keeping the handle low to the stone instead of raising it to 'arc' to the tip. Even doing that, it'll still be much less work than completely regrinding a new scandi-beveled edge where a fully-functional scandi edge already exists. Especially on this blade with the relatively small amount of tip damage, it wouldn't take as much time or be as dependent on sharpening skill to do it right. This is a no-brainer. In fact, I'd bet the maker would take the same approach, were it to be sent back for repair.

With this type of steel (non-stainless with little/no hard carbide content), even a decent mill file could be used to do the same thing, with the blade clamped into a vise (spine UP), and filing from the spine's rear to the tip. A coarse stone in SiC or aluminum oxide could be used the same way.

 

[Chris "Anagarika"]

Agree. Without raising the handle but focusing pressure (with wooden dowel) on the tip area will bring the full spine flat but angled downward in fractions of degree and still flat. Didn’t think of it that way.

 

[Deboelduncan]

Yes I do think I'll go with your idea David!

and to reply to you Chris, sending it back to the maker is not a very good idea I believe.. Marko (the current blacksmith at Kainuun puukko) works all by himself so waiting times are up, I think I'd have to wait a really long time for it to get back to me again. (I waited over a year on the knife after ordering)

many thanks for all the helpful replies guys! I'll post a picture when I'm done with it!

 

[jpm2]

When repairing broken tips, I sometime bring the edge to the spine, spine to the edge, or meet somewhere inbetween, just depends on the knife I'm repairing and how it mainly gets used, and how much an acute tip is needed.